fixed vs. rectracts ... Drag and turbulence

[Dean Pappas]

Hi Wayne,
 
Here's what little I know from both a theoretical and practical basis.
 
In general, our open wheel wells stink! 
They are draggy and may cause all kinds of turbulence.
Some ar worse than others, and there is no easy way, short of a flight test or wind tunnel,
of telling which setups will be cleaner. 
Tricycle-geared retracts are generally better than tail-draggers because the wheel wells are aft
of the wing's high-point.
 
According to one "real" aerodynamicist I spoke to, the best setups for drag reduction are in order:
1) retracts with good tight fitting doors. 
2) cleanly faired fixed gear.
3) retracts the way we presently do them.
4) crude fixed gear.
5) and retracts with poorly fitting doors can possibly end up being horrible!
 
As far as turbulence goes:
Our open wheel wells in the leading edge made this guy cringe!
He warned that poorly located fixed gear can cause turbulence with the flow under the wing root.
 
Now from a practical point, I can recount my own experiments and one done by Jim Martin
about a million years ago. (okay in the early seventies!)
 
I have taped the wheel wells over and put small streamlined tires on both my JEKYLL ( about 4 years ago) 
and an old tail-dragger TIPORARE (after the Tangerine contest in '83). Both planes showed no discernable speed
difference, but there was no fancy instrumentation. The JEKYLL flew the same, but I thought that
the TIPO (named TURNARARE) rolled more nicely. I thought that the transition, as I started to apply 
the down pressure in a slow roll, went more smoothly. I eventually discovered that a slack piece of tape 
across the wheel well in the area of the wire strut gave me the same benefit. Other builders make very 
shallow and narrow troughs for the wire, probably for the same reason. Since I fly from fairly rough grass,
the tape allowed more strut bend without binding. 
 
Experiments with big P-51 style gear doors on the Jekyll showed that it was affected horribly by turbulence
with the gear down, with or without the wells taped over. Result? Pants and legs should be as small as practical.
 
Jim Martin (team member in '73) put heavy duct-tape over the  wheel wells of his BANSHEE when he forgot
the air pump for his Rhom-Airs. Just last year, he told me that he thought the plane flew maybe a tiny bit 
better, despite the heavy tape. 
 
 
I hope this muddies the waters adequately,
    Reagards
    Dean P.
 

-----Original Message-----
From: Wayne Galligan [mailto:wgalligan at goodsonacura.com]
Sent: Thursday, July 17, 2003 4:23 PM
To: discussion at nsrca.org
Subject: fixed vs. rectract l.g.



Ok now. lets get down to the aerodynamic aspect of the rectract vs. fixed gear.  Anyone have some valid plus/minus on the two.  
 
WG


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